This invention relates to a Hall element and, more particularly, to highly coercive Hall element prepared by bonding magnetic material to a Hall element chip, and also to the method of manufacturing the same. In the conventional highly coercive Hall element prepared from a semiconductor substrate of, for example, gallium arsenide, a magnetic body, which consists of a chip obtained from a solid substrate fabricated by baking ferrite in the form of a plate, is joined to the underside of the Hall element chip, in order to increase the coercive force of the Hall element.
Furthermore, in order to increase the coercive force in the magnetic circuit of the Hall element, a material has been prepared from a resin containing magnetic powder of low hysteresis and high magnetic permeability for joining to the surface of the Hall element chip.
The above-mentioned type of Hall element was fabricated by way of the undermentioned steps.
First, a soldering agent such as gold or germanium is mounted on a semiconductor substrate. The soldering agent is thermally melted, and a magnetic chip diced from a solid substrate of ferrite is mounted thereon. Then, soldering agent, again of gold or germanium, is mounted on the magnetic chip, and is fused.
A Hall element chip diced from a semiconductor wafer constituting the Hall element is placed on the magnetic chip, and a circuit pattern formed on the substrate is connected to the Hall element chip by gold wire bonding.
Lastly, a silicon encapping agent mixed with magnetic powder is dripped on the surface of the Hall element chip. The mass is hardened to provide magnetic powder-containing resin. Later, the resin is hermetically sealed.
However, the above-mentioned Hall element and the method of manufacturing the same are accompanied with the undermentioned difficulties. The magnetic chip is diced from the solid substrate. The magnetic chip and the Hall element chip are separately mounted, resulting in complexity of assembly. Therefore, such a Hall element is undesirably expensive and ill-suited for mass production.
Some concrete drawbacks, will now be described in more detail. For example, if misalignment occurs during the mounting of the Hall element on the magnetic chip, this may cause the Hall element to break off from the magnetic chip; the yield is consequently reduced; noticeable variations appear in the Hall output voltage and product sensitivity; and the conventional soldering agent applied when mounting the Hall element on the magnetic chip may undesirably cause the Hall element to easily detach from the chip. Any or all of these problems inevitably increase the cost of production.
The magnetic chip is obtained from a solid substrate which is prepared by baking ferrite formed in the shape of a plate. Baked ferrite is, however, quite brittle and cannot be made into thin sheets. Moreover, the thickness of the baked ferrite cannot be freely chosen, thereby limiting the degree of latitude as regards choosing the level of sensitivity of Hall element.
It is impossible with the existing production technique to reduce the thickness of a backed solid ferrite substrate to less than 0.2 mm. Consequently, a magnetic chip, which is sufficiently thin, cannot be produced. When, therefore, the Hall element is mounted on the magnetic chip, the height from the substrate to the Hall element chip is undesirably increased, presenting difficulties in adjusting a wire loop to an appropriate shape at the time of wire bonding. Consequently, bonding wire often tends to detach from its bonding, thereby reducing the manufacturing yield of the Hall element and reducing its reliability.
When it is assembled as part of a motor, the Hall element should be made as thin and as small as possible. However, due to the appreciable thickness of the magnetic chip, the conventional Hall element presents significant disadvantages as regards the possibility of miniaturization and reduction of its thickness.